Characterization of Biocompatible Parylene-C Coatings for BIOMEMS Applications

Biological Micro-Electro-Mechanical Systems (BioMEMS) is one of the forefronts of research for adapting MEMS to meet demands for biological applications. The immense popularity of BioMEMS lies in the promise of rapid, accurate diagnostic results while requiring an exponentially lower sample volume which are achieved by replicating laboratory functionalities onto packaged miniaturized devices. These devices are usually fabricated using more than one material not necessarily bio-compatible which requires additional processing steps before they can be used for biological applications. A favorable solution is depositing a biocompatible coating. Further, improvements in our everyday life can already be felt from existing BioMEMS devices ranging from home pregnancy test [1] or lower volume blood analysis cartridge system [2], to prototype devices that can preemptively check for signs of osteoporosis [3] within minutes. However, other applications such as bio-device for testing blood glucose level demands quicker results in seconds with high accuracy for saving patients with diabetes from suffering a coma. The ever growing demands for more functionalities and/or higher efficiency and throughput can be met by high aspect ratio microstructures (HARMS) [4] and surface modification/ functionalization. Higher height-to-width aspect ratio allows greater number of structures to be fabricated per area which provides tighter packaging of devices and further reducing the sizes of BioMEMS devices [5, 6, 7, 8, 9]. Furthermore, HARMS increase the surface area of devices over common aspect ratio structures (2-5) which allows for higher throughput. In addition, modification of surface energy and roughness of HARMS can functionalize the device by tailoring the aforementioned parameters to promote and/ or prevent cells/proteins adhesion. The power of miniaturization and the inclusion of HARMS as highlighted by the given examples are beneficial for BioMEMS; however, the fabrication of these devices using the state-of-the-art microfabrication technology usually involves more than one material [4,10]. In order to not add any extra parameters, bio-researchers ideally yearn for devices of a single material surface that will have minimum interactions with the sample and its chemicals. An optimal solution is to use a biocompatible, highly conformable, and pinhole-free coating uniformly deposit on HARMS and therefore allowing samples and/or chemicals to interact with only the coating surface. Parylene, traditionally known in MEMS for possessing barrier property, is such a coating material which possesses all the above properties as well as being chemically inert, lightweight, transparent, of high dielectric strength and many other properties that are favorable for various BioMEMS applications [6,17].